ch-6-w-12-gas turbines.pptx

7/24/2019 Ch-6-W-12-Gas Turbines.pptx

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h-6-W-12

Gas Turbines

1


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2

Turbines as potential power plants

Operation and characteristics of turbines

Performance calculations

Radial flow turbines

Radial axial flow and mixed flow turbines

Turbines applicable to AFVs

Comparison of turbines with diesel engines

Comparison of fuel consumption at different loads


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3

Direct Drive and Mechanical Drive

With land based industries, gas turbines can be used in either direct drie or

mechanical drie application!

With power generation, the gas turbine shaft is coupled to the generator shaft,

either directl" or ia a gearbox# $direct drie% application!A gearbox is necessar" in applications where the manufacturer offers the

pac&age for both '( and )( c"cle *+ert, +- applications! The gear box will

use roughl" ./ of the power deeloped b" the turbine in these cases!

For mechanical drive applications, the turbine module arrangement is

different! 0n these cases, the combination of compressor module, combustormodule, and turbine module is termed the gas generator! 1e"ond the turbineend of the gas generator is a freely rotating turbine! 0t ma" be one or morestages! 0t is not mechanicall" connected to the gas generator, but instead is

mechanicall" coupled, sometimes ia a gearbox, to the e2uipment it is driing!

Compressors and pumps are among the potential $drien% turbomachiner"items


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4

Direct Drive and Mechanical Drive..The mechanical drie gas turbines are aailable in three configurations#

3! 4ingle spool5integral output shaft,

.! 4ingle spool5split output shaft, and

6! 7ual spool5split output shaft!

.0n a single spool-integral output shaft unit the output shaft is an extensionof the main shaft, which connects the compressor and turbine components!

The output shaft ma" be an extension of the turbine shaft or it ma" be an

extension of the compressor shaft!

.When the output drie shaft is an extension of the turbine component shaft itis referred to as a $ hot end drive!% 8i&ewise, when the output drie shaft isan extension of the compressor component shaft it is referred to as a $ coldend drive.

.There are disadantages to each configuration!


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6

Operation and

characteristicsof turbines


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9as turbines usuall" operate in an open c"cle as shown!

The" can be modeled as a closed c"cle b" utiliing the air5standard

assumptions!

The combustion and the exhaust process are replaced b"

a! A constant pressure heat addition from an external source !

b! A constant pressure heat5re:ection process to the ambient air!

BRAYTON Y LE-

The ideal gas turbine cycle.

7


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The ideal c"cle that the wor&ing fluid

undergoes in this closed loop is the 1ra"ton

c"cle, which is made up of four internall"

reersible processes#

1 ! isentropic compression

"! constant pressure heat addition

" #! isentropic e$pansion %in turbine&

# 1! constant pressure heat re'ection.

8


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9


10/50

($ample-1. The )imple *deal +rayton CycleA gas5turbine power plant operating on an ideal 1ra"ton c"cle has a

pressure ratio of ;! The gas temperature is 6(( < at the compressor inlet

and 36(( < at the turbine inlet! =tiliing the air5standard assumptions,

determine *a- the gas temperature at the exits of the compressor and theturbine,

*b- the bac& wor& ratio, and

*c- the thermal efficienc"!

10


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11

)olution. ,ith constant specific heats..

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Deviation of ctual /as-Turbine Cycles from *deali0ed OnesThe actual gas5turbine c"cle differs from the ideal 1ra"ton c"cle on seeral

accounts!

3! 4ome pressure drop during the heat5addition and heat re:ection

processes is ineitable!

.! The actual wor& input to the compressor is more, and

6! The actual wor& output from the turbine is less because of irreersibilities!

>! The deiation of actual compressor and turbine behaior from the

idealied isentropic behaior can be accuratel" accounted for b" utiliing

the isentropic efficiencies of the turbine and compressor as

where states .a and >a are the actual exit states of

the compressor and the turbine, respectiel", and

.s and >s are the corresponding states for the

isentropic case!

12


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($ample-. The )imple ctual +rayton CycleA gas5turbine power plant operating on an actual 1ra"ton c"cle has a


and 36(( < at the turbine inlet! =tiliing the air5standard assumptions, and

assuming a compressor efficienc" of ;( percent and a turbine efficienc" of;) percent, determine

*a- the bac& wor& ratio,

*b- the thermal efficienc", and

*c- the turbine exit temperature

13


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T( +23TO4 C3C5( 6*T 2(/(4(2T*O4

The high5pressure air leaing the compressor can be heated b" transferring

heat to it from the hot exhaust gases in a counter5flow heat exchanger, which

is also &nown as a regenerator or a recuperator!

sassu#ptionstandardairco$dunder

esseffectientheca$$edis

rre&eneratoidea$anapproachesre&enatorawhiche'tent toThe

and,

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14


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($ample-". The )imple *deal +rayton Cycle ,ith regeneration

A gas5turbine power plant operating on an actual 1ra"ton c"cle has a


and 36(( < at the turbine inlet! =tiliing the air5standard assumptions, andassuming a compressor efficienc" of ;( percent and a turbine efficienc" of

;) percent!

7etermine the thermal efficienc" of the gas5turbine if a regenerator haing

an effectieness of ;( percent is installed!

15


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The +rayton cycle ,ith *ntercooling7 2eheating7 and 2egeneration

The wor& re2uired to compress a gas between two specified pressures can be

decreased b" carr"ing out the compression process in stages and cooling the gas in

between?that is, using multistage compression with intercooling!

As the number of stages is increased, the compression process becomes nearl"

isothermal at the compressor inlet temperature, and the compression wor&

decreases!

8i&ewise, the wor& output of a turbine operating between two pressure leels can be

increased b" expanding the gas in stages and reheating it in between?that is,utiliing multistage expansion with reheating! This is accomplished without raising the

maximum temperature in the c"cle!

As the number of stages is increased, the expansion process becomes nearl"

isothermal!

The foregoing argument is based on a simple principle# The steady-flow

compression or expansion work is proportional to the specific volume of the

fluid! Therefore, the specific olume of the wor&ing fluid should be as low as possible

during a compression process and as high as possible during an expansion process!

This is precisel" what intercooling and reheating accomplish!16


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These are two other common techni2ues for increasing the thermal efficienc"

of the gas turbine c"cle!

3

4

1

2

P

P

P

P=

17

1. *nter-CoolingAn intercooler can be inserted into the compressionprocess@ air is compressed to an intermediate

pressure, cooled in an intercooler, and then

compressed to the final pressure! This reduces the

wor& re2uired for the compressor, and it reduces the

maximum temperature reached in the c"cle! Theintermediate pressure is determined b" e2uating the

pressure ratio for each stage of compression@


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.! 2eheating .The second techni2ue for increasing thermal efficienc" is touse a second combustor, called a reheater! The intermediate pressure is

determined as in the compressor@ we again re2uire that the ratios be e2ual@

that is,

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0f the number of compression ande$pansion stages is increased, theideal gas5turbine c"cle with

intercooling, reheating, andregeneration approaches the (ricssoncycle, as illustrated in Fig!

And the thermal efficiencyapproaches the theoretical limit %the

Carnot efficiency&.

+oweer, the contribution of each additional stage to the thermal

efficienc" is less and less, and the use of more than two or three stages

cannot be :ustified economicall"!

Finall", we should note that intercooling and reheating are never used,ithout regeneration! 0n fact, if regeneration is not emplo"ed,intercooling and reheating reduce the efficienc" of a gas5turbine c"cle!

20


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(8M95(-#. /as Turbine ,ith 2eheating and *ntercoolingAn ideal gas5turbine c"cle with two stages of compression and two stages of

expansion has an oerall pressure ratio of ;! Air enters each stage of the

compressor at 6(( < and each stage of the turbine at 36((

a! The bac& wor& ratio and,b! The thermal efficienc" of this gas5turbine c"cle,

Assuming

*a-no regenerators and

*b- an ideal regenerator with 3(( percent effectieness!Compare the results with those obtained in xample53!

21


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22

)olutionFor two5stage compression and expansion, the

wor& input is minimied and the wor& output is

maximied when both stages of the compressor

and the turbine hae the same pressure ratio!

Thus,

Air enters each stage of the compressor at the same temperature, and each stage hasthe same isentropic efficienc" *3(( percent in this case-! Therefore, the temperature

*and enthalp"- of the air at the exit of each compression stage will be the same! A

similar argument can be gien for the turbine!

=nder these conditions, the wor& input to each stage of the compressor will be the

same, and so will the wor& output from each stage of the turbine!

)olution


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23

)olution..*a- *n the absence of any regeneration

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24

)olution*a- *n the absence of any regeneration

A comparison of these results with those obtained in

xample 53 *single stage compression andexpansion- reeals that multistage compression with

intercooling and multistage expansion with reheating

improe the bac& wor& ratio *it drops from >( to 6(!)3

/- but hurt the thermal efficienc" *it drops from >) to

6;!6/-!

Therefore, intercooling and reheating are notrecommended in gas5turbine power plants unless

the" are accompanied b" regeneration!

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25/50

25

)olution..*b- 6ith ideal regeneration

The addition of an ideal regenerator *no pressure drops, 3(( / effectieness-

does not affect the compressor wor& and the turbine wor&! Therefore, the net wor& output and the bac& wor& ratio of an ideal gas5turbine c"cle

are identical whether there is a regenerator or not! A regenerator, howeer, reduces the heat input re2uirements b" preheating the air

leaing the compressor, using the hot exhaust gases! 0n an ideal regenerator, the compressed air is heated to the turbine exit

temperature TBbefore it enters the combustion chamber!

Thus, under the air5standard assumptions, h)

hD

hB

!

The heat input and the thermal efficienc" in

this case are

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($ample-:A gas turbine c"cle ta&es in air at .)( C and atmospheric pressure! The

compression pressure ratio is >! The compressor efficienc" is D)/! The inlet

temperature to turbine is limited to D)((C! What turbine efficienc" would gie

oerall c"cle efficienc"(/E

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Compressor

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($ample-;0n a simple gas turbine plant air enters the compressor at .D (C and 3 bar! 0t is

then heated in the combustion chamber to D(((C and then enters the turbine

and expands to 3 bar! The isentropic efficienc" of compressor and turbine are

(!;( and (!;) respectiel" and the combustion efficienc" is (!B;! The fall in

pressure in the combustion chamber is (!3 bar! 7etermine*a- The thermal efficienc"!

*b- The bac& wor& ratio!

*c- The wor& ratio

*d- The air rate in &g&Whr

*e- The specific fuel consumption*f- The air5fuel ratio

For air, Cp3!(() &G&g!

For combustible gas Cp3!3>D &G&g!.D(( &G&g

($ample-


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($ample-, calculate the isentropic efficienc" of turbine for a plantthermal efficienc" of (!.B


For combustible gas Cp3!(D &G&g!


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($ample-=An open c"cle gas turbine plant has a 35stage compressor and turbine

incorporating a heat e$changer! The air suction is at 3 bar and .B( !) and shaft output of >((( &W, the mass flow is >(

&gs! 0f the thermal ratio of heat exchanger is (!' and isentropic efficienc" of

compressor is (!;>, calculate the isentropic efficienc" of turbine for a plantthermal efficienc" of (!.B


For combustible gas Cp3!(D &G&g!


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($ample-> Compound /as Turbine0n a compound gas turbine, the air from the compressor passes through a heat

exchanger heated b" the exhaust gases from the low pressure turbine, and

then into the high pressure combustion chamber! The high pressure turbine

dries the compressor onl"! The exhaust from the +P turbine passes through

the 8P combustion chamber to the 8P turbine which is coupled to the externalload! The following data refer to the plant#5

Compression ratio >

0sentropic efficienc" of compressor (!;'

0sentropic efficienc" of +P turbine (!;>

0sentropic efficienc" of 8P turbine (!;(Iechanical efficienc" of drie to compressor(!B.

+eat exchanger effectieness (!D

Temp! of gases entering +P turbine '((C

Temp! of gases entering 8P turbine '.)(C

For air, Cp3!(() &G&g!For combustible gas Cp3!3) &G&g!


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Ch-6-W-12-Gas TurbinesProf (Col) GC ishra

31

($ample-1? utomotive /as Turbine ,ith .( and po,er turbineThe la"out of an automotie gas turbine is shown in the figure! A .5stage

compressor with an oerall pressure ratio of ' is drien b" a +P turbine! The

8P turbine proides motie power to the car! A heat exchanger with (!')

effectieness is proided! The air inlet to 8P compressor is 3)(C and the +P

turbine inlet temperature is ;(((C! The mass flow is (!D &gs!0sentropic efficienc" of compressor (!;

0sentropic efficienc" of each turbine (!;)

Iechanical efficienc" of compressor shaft (!B.

Combustion efficienc" (!BD

Temp! of gases entering +P turbine '((CCV of fuel >.'(( &G&g

7etermine,

*a- The net power deeloped *b- The oerall thermal efficienc" *c- The specific

fuel consumption!

($ample-11 /as Turbine ,ith ( and po,er turbine


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($ample 11 /as Turbine ,ith .( and po,er turbine0n an open circuit gas turbine, plant air is compressed adiabaticall" from a

temperature of 3)(C in an axial flow compressor, the pressure ratio being >

and the adiabatic efficienc" of compression is (!;>! The air is then split into

two streams which flow to separate combustion chambers in which

temperature of the air is raised to ')((C!The product of one combustion chamber expands adiabaticall" in a turbine

whose power is :ust sufficient to drie the compressor@ the adiabatic efficienc"

of expansion being (!;;! The product of the combustion in other combustion

chamber expand adiabaticall" in a power turbine of efficienc" (!;) which

dries an electric generator of efficienc" (!B)!stimate,

*a- The ratio of the air passing through power turbine to the total air

compressed!

*b- The rate at which air is compressed!

*c- The thermal efficienc" of the plant when the output from the generator is>((( &W!

Jeglect drop in pressure in ducts and pipes, increase in the mass flow rate

due to addition of fuel and mechanical losses!

Cp for air3!(() and for gases3!33 and Cp5C(!.;D &G&g!< at all points in

the plant!

The Turbines


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33

The TurbinesT,o +asic Types - 2adial and $ial Almost all industrial 9as Turbines use

axial flow turbines

5i@e the Compressor7 Turbine

($pansion Ta@es 9lace in A)tages a row of stationar" blades *noles-

followed b" a row of moing blades

one stage!

2adial Blo, Turbines


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2adial Blo, Turbines


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35

$ial Blo, Turbines


36/50

36

$ial Blo, TurbinesAxial flow turbines are the most widel" used@ except on low power turbines!

The" are more efficient than the radial flow turbines in most operational ranges!

There are three types of a$ial flo, turbine# impulse, reaction, and a

combination of the two &nown as impulse5reaction!

0n the impulse type the total pressure drop across each stage occurs in thefixed nole guide anes, which, because of their conergent shape,

increase the gas elocit" while reducing the pressure! The gas is directed

onto the turbine blades which experience an impulse force caused b" the

impact of the gas on the blades!

0n the reaction type the fixed nole guide anes are designed to alter thegas flow direction without changing the pressure! The conerging blade

passages experience a reaction force resulting from the expansion and

acceleration of the gas!

Jormall" gas turbine engines do not use pure impulse or pure reaction

turbine blades but the impulsereaction combination *Figure5next slide-!The proportion of each principle incorporated in the design of a turbine is

largel" dependent on the t"pe of engine in which the turbine is to operate,

but in general it is about )(/ impulse and )(/ reaction!

Comparison bet,een


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37

Comparison bet,eena pure impulse turbine

andan impulsereaction turbine.

utomotive /as Turbines


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38

dvantages over *C engines!-

3! 9as turbine c"cle offers the thermod"namic adantage of complete expansion!

.! 4implicit"! Fewer moing parts@ 9T directl" produces relatie power!

6! 4mooth and ibration5less power delier"! 7ue to rotar" action! Also, combustion

generated noise is absent due to continuous combustion!

>! Ver" compact and light for a specific power *sp! Weight 3(5.(/ less than 40 engine-!

)! Potential for low emissions due to the isolation process from the components where

wor& transfers ta&e place, permitting better control!

'! Potential for lower maintenance re2uirements and better life expectanc" due to lower

number of moing parts *about .6rdof 40 engines-!

D! as" cold starting!

;! Cooling s"stem is not re2uired in a simple gas turbine!

B! Jegligible lubricating oil re2uirement!

3(!+igh mechanical efficienc" *;)5B(/-!33! Cheaper fuels ma" be used!

utomotive /as Turbines


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39

Disadvantages !-

3! 0n spite of complete expansion, the thermal efficienc" of the 9T is lower than piston

engines because of lower temperatures and lower compressor efficienc" *max! ;(/

for the best rotar" compressors-!

.! Therefore, with a simple 9T unit *without a heat exchanger-, the sfc ma" be twicethat of aerage petrol engine and thrice that of diesel engine!

6! Automotie engines for most part run on part load! The efficienc" of 9T under part

load conditions is er" poor!

>! The speed of 9T rotor is er" high *greater than 6(((( rpm-! This necessitates a

large gear reduction!)! +igh speeds also result in high rotational inertia which creates difficulties in throttle

control due to time5lag!

'! +igh initial cost due to costl" materials and R K 7 and manufacturing cost! Presentl"

the cost is about twice that of petrol engines!

D! The characteristics li&e specific power, acceleration, fuel econom", relatie cost etc!worsen with decreasing sie!

Configuration


40/50


40

g1.)ingle-shaft /as Turbine


41/50


41

. Bree or7 T,in-shaft /as Turbine-Iost suitable for automotie applications

M11 brams - (ngine


42/50

42

g

A9T3)(( turboshaft engine from

+one"well!

Compact design, cold5starting,

instant power, multifuel capabilitiesand stealth" operation!

The A9T53)(( turbine output shaftLs

speed is reduced b" a gearbox!

This reduces the wor& turbineLs

approximate .''(( rpm maximumangular speed to an output shaft

maximum speed of 6)(( rpm!

The output shaft of the gear

reduction dries the tor2ue

conerter


43/50


43

The transmission module used in the I3A3 houses the tor2ue conerter


44/50


44

The transmission module used in the I3A3 houses the tor2ue conerter,

transmission, a h"drostatic steering unit, and h"draulic bra&es! Figure

illustrates the oerall la"out of the transmission module!

GAS TURBINE (GT) VS DIESEL ENGINES


45/50

( )

1. 6eight Comparison

/T-1:?? % M11 bram & ! 11 g ,o starter7generator

EC2-1";? % /M & ! ?> @g ,ith starter7generator and cooling system

M+-=


46/50

. )pecific fuel Consumption %sfc&.

/T-1:?? ! ?# gmbhphr

EC2-1";? ! 1=?

M+-=


47/50

". ir reFuirement

A9T53)(( re2uires approx! 6 times more air for combustion than AVCR5

36'(@ correspondingl" larger re2uirement of air cleaner!

9as turbines re2uire less cooling than diesel engines because their heatre:ection is onl" 3(5.(/ that of diesel! 1ut, depending upon the total air

re2uirement for cooling the power pac& including the transmission, there is

no significant difference to affect the inlet and outlet grills which are

goerned b" the total air mass flow!

The amount of air re2uired for cooling is also important for its influence onthe power re2uired for driing the cooling fan!

A9T53)(( 6( hp to cool onl" the engine!

AVCR536'( 3'( hp

A9T53)(( )( hp for .5stage cooling s"stem *engine

and Transmission-!

AVCR536'( .)( hp

47



48/50


#. gility

As a corollar" to less power absorbed b" cooling fans of A9T53)((, it is

claimed that this gae the turbine powered I3A3 significantl" better

acceleration since it had more power aailable at the sproc&ets!

/T '!. to '!D 4ec for acceleration from ( to 6. &mph

EC2 D!; to ;!D 4ec

M+ =


49/50

M )tarting.

- +etter starting for /T especially on cold conditions.

- /T reFuires lesser starting torFue.

M 4oise./T Fuieter than diesel but7 militarily less significant since7 ma'or source ofnoise is due to trac@s.

M )mo@e (mission./Ts due to their continuous combustion at large B ratio produce less [email protected],ever diesel ,ith pre combustion chambers can achieve good results.

M 2M-D.

/T is simpler since it has "?G less components.

Time bet,een overhauls for /T is in the range of 1:7???-?7??? m asagainst :7???-G

better for diesels if only the critical defects are considered.M Cost.

/T costlier due to reFuirement of more e$pensive materials and highercapital investment in production plant % /T costlier by appro$ H ;?7??? thanEC2-1";?&.

"erf!r#ane

49

Th E '


50/50

T$AN%

&OU

The En'

UESTIONS **

ON LUSION

ch-6-w-12-gas turbines.pptx

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